HR: 0800h
AN: T21B-0528    [Abstracts]
TI: Constructing a 3D Dynamic Model of Mantle Wedge Under the NE Honshu Subduction Zone, Japan
AU: * Honda, S
EM: honda@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1,Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Yoshida, T
EM: tyoshida@mail.tains.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Aramaki-aza-Aoba, Aoba-ku, Sendai, 980-8578 Japan
AB: In our previous studies, we propose an existence of small-scale convection under the NE Honshu subduction zone, Japan, to explain the origin of hot fingers. In this presentation, we refine our model by comparing the model results with the geophysical and geologic data observed there. Assuming that the temperature anomalies have a close connection with the seismic anomalies, we constrain the geometry of the low viscosity wedge (LVW) overlying the slab, which may be produced by the water dehydrated from the subducting slab. Our preferred model suggests step-like low velocity anomalies above the subducting slab rather than smooth anomalies subparallel to the subducting slab, since the shallow nature of the LVW is required for the small-scale convection to occur at the back-arc end of the LVW. A movement of cold plumes generated at the back-arc end of the LVW may be related to a possible migration of volcanism from back-arc to volcanic front side. To be consistent with the observation, which may suggest the migration rate of $_Lsim$ 2 cm/yr, models require weak couplings between the mantle wedge and the underlying subducting slab, whose speed of subduction is $_Lsim$ 10 cm/yr. 3D calculations of our final model show fairly continuous and strong temperature anomalies (several hundreds degrees) under the volcanic front and weak finger-like temperature anomalies (several tens degrees) behind them, which are similar to the pattern of the seismic tomography. The time-dependent behavior of the temperature field shows that the pattern of fingers flip-flops with a time-scale equal to the ratio of the horizontal extent of the LVW to the migration speed of cold plumes. This change of pattern of fingers may have an important implication for understanding the past distribution of volcanism.
DE: 8100 TECTONOPHYSICS
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting